Vulcanizable fluororubber composition

ABSTRACT

A vulcanizable fluororubber composition which contains 
     (a) an iodine- and/or bromine-containing fluororubber, 
     (b) a vulcanizing agent which is an organic peroxide, and 
     (c) a compound of the formula: ##STR1## wherein R 1  and R 2  each is an alkyl group having 1 to 3 carbon atoms, in an amount of 0.05 to 5 ppm based on the fluororubber (a) gives a transparent colorless vulcanized material.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a vulcanizable fluororubber compositionwhich gives a colorless cured material.

2. Related Art

In the field of the preparation of a semiconductor, a vulcanizedfluororubber is used as a sealing material for an instrument forgenerating plasma. The conventional sealing material has the problemsthat the particles are generated and that the leakage is caused by thedeterioration of the sealing material. Preferably, the sealing materialcontains no filler and is transparent so that the dust is visible.However, when the filler is merely excluded, the vulcanized fluororubberbecomes transparent brown or opaque brown so that it cannot betransparent colorless.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a fluororubbercomposition which gives a transparent colorless vulcanized material.

The present invention provide a vulcanizable fluororubber compositioncomprising:

(a) an iodine- and/or bromine-containing fluororubber,

(b) a vulcanizing agent which is an organic peroxide, and

(c) a compound of the formula: ##STR2## wherein R¹ and R² each is analkyl group having 1 to 3 carbon atoms, in an amount of 0.05 to 5 ppmbased on the fluororubber (a).

DETAILED DESCRIPTION OF THE INVENTION

The iodine- and/or bromine-.containing fluororubber (a) is a polymer inwhich an iodine and/or bromine atom in an amount of 0.001 to 10% byweight, preferably 0.01 to 5% by weight is bonded to a carbon atom of afluorine-containing polymer. Although the carbon atom to which theiodine and/or bromine atom is bonded is preferably an end of a polymerchain, the present invention is not limited to this so that the carbonatom bonding to the iodine and/or bromine atom may be the carbon atom inthe main chain, the branch chain or the branch point.

The iodine- and/or bromine-containing fluororubber (a) means afluorinated polymer having rubber-like elasticity at a room temperatureafter the vulcanization. A fluororubber includes any of conventionallyknown fluororubbers. Typical examples of the fluororubber arefluororubbers such as a vinylidene fluoride/hexafluoropropylene; polymer(a preferable molar ratio of vinylidene fluoride to hexafluoropropyleneis from 45:55 to 95:5), a vinylidenefluoride/tetrafluoroethylene/hexafluoropropylene polymer (a preferablemolar ratio of vinylidenefluoride/tetrafluoroethylene/hexafluoropropylene is 25-90:1-35:1-50), avinylidene fluoride/chlorotrifluoroethylene polymer, atetrafluoroethylene/propylene polymer, a hexafluoropropylene/ethylenepolymer, a perfluoroalkyl vinyl ether (which includes a plural of etherlinkages)/olefin (for example, tetrafluoroethylene, ethylene and thelike) polymer (a preferable molar ratio of the perfluoroalkyl vinylether to the olefin is from 15:85 to 75:25), a fluorosilicone polymer, afluorophosphazene polymer and the like. The examples of the iodine-and/or bromine-containing fluororubber (a) are described in, forexample, U.S. Pat. Nos. 4,243,770, 4,035,565 and 4,214,060 (thedisclosures of which are incorporated herein by reference), JapanesePatent Kokai Publication No. 125491/1978, Japanese Patent KokokuPublication No. 4115/1978 and Japanese Patent Kokai Publication No.20310/1984. The iodine- and/or bromine-containing fluororubber (a) canbe prepared by, for example, adding an iodine- and/or bromine-containingcompound (for example, ICH₂ CF₂ CF₂ OCF═CF₂ and the like) to the abovemonomers (for example, vinylidene fluoride and the like) and conductingthe polymerization. The iodine- and/or bromine-containing fluororubber(a) usually has a molecular weight of 1,000 to 1,000,000.

The vulcanizing agent (b) is not limited, insofar as it is the organicperoxide. Specific examples of the vulcanizing agent (b) are1,1-bis(t-butylperoxy)-3,5,5-trimethylcyclohexane,2,5-dimethylhexane-2,5-dihydroxyperoxide, di-t-butyl peroxide, t-butylcumyl peroxide, dicumyl peroxide,α,α-bis(t-butylperoxy)-p-diisopropylbenzene,2,5-dimethyl-2,5-di(t-butylperoxy)hexane,2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3, benzoyl peroxide,t-butylperoxybenzene, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane,t-butylperoxymaleic acid, t-butylperoxyisopropyl carbonate and the like.The amount of the vulcanizing agent (b) is from 0.1 to 5.0 parts byweight per 100 parts by weight of the fluororubber (a).

The component (c) is the compound of the formula (I) which acts as astabilizing agent. Specific examples of the compound (I) are2-t-butyl-4-methoxyphenol (m-t-butyl-p-hydroxyanisole),3-t-butyl-4-methoxyphenol, 2-t-butyl-4-ethoxyphenol,3-t-butyl-4-ethoxyphenol, 2-t-butyl-4-propoxyphenol,3-t-butyl-4-propoxyphenol, 2-(1,1-diethylpropyl)-4-methoxyphenol, 3-(1,1-diethylpropyl)-4 methoxyphenol, 2-(1,1 -dipropylbutyl)-4-methoxyphenol,3-(1,1-dipropylbutyl)-4-methoxyphenol, 2-(1,1-diethylpropyl)-4ethoxyphenol, 3-(1,1 -diethylpropyl)-4-ethoxyphenol,2-(1,1 -dipropylbutyl)-4-ethoxyphenol, 3-(1,1-dipropylbutyl)-4-ethoxyphenol, 2-(1,1-diethylpropyl)-4-propoxyphenol,3-(1,1 -diethylpropyl)-4-propoxyphenol and the like. The amount of thecomponent (c) is from 0.05 to 5 ppm, preferably from 0.5 to 2.5 ppmbased on the fluororubber (a).

The composition of the present invention may contain a crosslinking aid(d). The crosslinking aid (d)is basically effective, when it has thereaction activity to a peroxy radical and a polymer radical. The type ofthe crosslinking aid (d) is not specifically limited. The crosslinkingaid (d) is usually a polyfunctional compound which contributes to thevulcanization by the radical functionality (for example, a compoundwhich contains at least two CH₂ ═CH--, CH₂ ═CH--CH₂ -- and/or CF₂ ═CF--groups). Preferable examples of the crosslinking aid (d) are triallylcyanurate, triallyl isocyanurate, triacryl formal, triallyltrimellitate, N,N'-m-phenylene bismaleimide, dipropargyl terephthalate,diallyl phthalate, tetraallyl terephathalamide, triallyl phosphate,hexafluorotriallyl isocyanurate and N-methyltetrafluorodiallylisocyanurate. The amount of the crosslinking aid (d) is usually at most10 parts by weight, preferably from 0.1 to 5.0 parts by weight per 100parts by weight of the fluororubber (a).

The composition may contain a small amount of an additive, if theadditive does not deteriorate the transparency. The composition maycontain a small amount of a colorant so as to color the composition (sothat the composition is transparent colored one).

The procedure for mixing homogeneously these components includes amethod comprising mixing the stabilizing agent (c) with the vulcanizingagent (b) and the optional crosslinking aid (d) and then using an openroll mill and a method comprising using a closed mixer such as akneader.

The vulcanization can be conducted under the usual vulcanizationconditions for the fluororubber. For example, the vulcanizablecomposition is mixed and charged in a mold, and the press vulcanizationis conducted by keeping the composition at 100°-200° C. and 20-100kg/cm² for 5-180 minutes and then the oven vulcanization is conducted bykeeping this composition at 150°-300° C. in an oven for 0-50 hours so asto give a vulcanized rubber.

The fluororubber composition of the present invention can be used in thefield in which the dust is extremely undesirable, particularly as asealing material in a plasma generation instrument for preparing asemiconductor. It can be used also in a food field and a medical field.

PREFERRED EMBODIMENT OF THE INVENTION

The present invention will be illustrated by the following Examples andComparative Examples which do not limit the present invention.

Example 1

Perhexa 2.5 B (manufactured by Nippon Oil & Fats Co. Ltd., an organicperoxide) (0.5 parts by weight) and triallyl isocyanurate (TAIC) (0.5parts by weight) containing m-t-butyl-p-hydroxyanisole (BHA) (250 ppm)(1.25 ppm based on the fluororubber) were mixed with Dai-el perflo GA-15[manufactured by Daikin Industries Ltd., an iodine-containingfluororubber (tetrafluoroethylene/perfluorovinylether copolymer)] (100parts by weight) by an open roll mill to prepare a composition.

The press vulcanization was conducted at 160° C. for 10 minutes and theoven vulcanization was conducted at 180° C. for 4 hours to prepare avulcanized rubber sheet (thickness: 2 mm). Various properties weremeasured according to JIS (Japanese Industrial Standard) K6301. Inaddition, the color of the fluororubber sheet after the vulcanizationwas observed. The results are shown in Table 1.

Examples 2 and 3 and Comparative Example 1

The same procedure as in Example 1 was repeated, except that componentsshown in Table 1 were used. Dai-el G-912 (manufactured by DaikinIndustries Ltd.) is an iodine-containing fluororubber (a vinylidenefluoride/tetrafluoroethylene/hexafluoropropylene copolymer), Dai-elG-902 (manufactured by Daikin Industries Ltd.) is an iodine-containingfluororubber (a vinylidenefluoride/tetrafluoroethylene/hexafluoropropylene copolymer), and BHT is2,6-di-t-butyl-4-methylphenol.

                  TABLE 1                                                         ______________________________________                                                  Ex. 1  Ex. 2    Ex. 3    Com. Ex. 1                                 ______________________________________                                        GA-15       100                      100                                      G-912                100                                                      G-902                         100                                             Perhexa 2.5B                                                                              0.5      0.5      0.5    0.5                                      TAIC (containing                                                                          0.5      0.25     0.5                                             250 ppm of BHA)                                                               TAIC (containing                     0.5                                      50 ppm of BHT)                                                                Properties                                                                    M.sub.100   19       9        11     18                                       T.sub.B     88       33       36     92                                       E.sub.B     260      550      620    250                                      H.sub.s     59       56       60     60                                       Color       Trans-   Trans-   Trans- Trans-                                               parent   parent   parent parent                                               colorless                                                                              colorless                                                                              colorless                                                                            brown                                    ______________________________________                                    

Comparative Example 2-6

The same procedure as in Example 1 was repeated to prepare thevulcanized rubber sheet, except that the type and amount of compoundsshown in Table 2 were used instead of 250 ppm ofm-t-butyl-p-hydroxyanisole. The color of the vulcanized rubber sheet wasobserved and a total light transmittance was measured. The total lighttransmittance was measured by DIRECT READING HAZE METER manufactured byTOYO SEIKI SEISAKUSHO, Ltd. The results are shown in Table 2, includingthe results of Example 1 and Comparative Example 1. TBH is2-t-butylhydroquinone.

                  TABLE 2                                                         ______________________________________                                                      Amount of             Total                                                   stabilizing           light                                     Stabilizing   agent (ppm)           trans-                                    agent in TAIC (based on             mittance                                  (Type, Amount)                                                                              fluororubber)                                                                            Color      (%)                                       ______________________________________                                        Ex.1  BHA 250 ppm 1.25       Transparent                                                                            85                                                                   colorless                                        Com.  BHT 50 ppm   0.25      Transparent                                                                            69                                      Ex. 1                        dark brown                                       Com.  BHT 300 ppm 1.5        Transparent                                                                            74                                      Ex. 2                        dark brown                                       Com.  BHT 500 ppm 2.5        Transparent                                                                            76                                      Ex. 3                        dark brown                                       Com.  TBH 300 ppm  0.25      Transparent                                                                            72                                      Ex. 4                        brown                                            Com.  TBH 500 ppm 2.5        Transparent                                                                            75                                      Ex. 5                        brown                                            Com.  None        0          Transparent                                                                            80                                      Ex. 6                        light brown                                      ______________________________________                                    

Example 4 and Comparative Examples 7 and 8

The same procedure as in Example 1 was repeated to prepare thevulcanized rubber sheet, except that the amount ofm-t-butyl-p-hydroxyanisole was as shown in Table 3. With respect to thevulcanized rubber sheet, the color was observed and the total lighttransmittance was measured. The results are shown in Table 3, includingthe results of Example 1 and Comparative Example 6.

                  TABLE 3                                                         ______________________________________                                        Amount of   Amount of                                                         stabilizing stabilizing                                                       agent (ppm) agent (ppm)           Total light                                 (content in (based                transmittance                               TAIC)       fluororubber)                                                                            Color      (%)                                         ______________________________________                                        Com.   0        0          Transparent                                                                            80                                        Ex. 6                      brown                                              Ex. 4                                                                                10       0.05       Transparent                                                                            83                                                                   colorless                                          Ex. 1                                                                               250       1.25       Transparent                                                                            85                                                                   colorless                                          Com.  3000      15         Transparent                                                                            82                                        Ex. 7                      brown                                              Com. 10000      50         Transparent                                                                            81                                        Ex. 8                      brown                                              ______________________________________                                    

What is claimed is:
 1. A vulcanizable fluororubber compositioncomprising:(a) an iodine- and/or bromine-containing fluororubber, (b) avulcanizing agent which is an organic peroxide, and (c) a compound ofthe formula: ##STR3## wherein R¹ and R² each is an alkyl group having 1to 3 carbon atoms, in an amount of 0.05 to 5 ppm based on thefluororubber (a).
 2. The composition according to claim 1, wherein theamount of the vulcanizing agent (b) is from 0.1 to 5.0 parts by weightper 100 parts by weight of the fluororubber (a).
 3. The compositionaccording to claim 1, wherein the fluororubber (a) is a polymer in whichan iodine and/or bromine atom in an amount of 0.001 to 10% by weight isbonded to a carbon atom of a fluorine-containing polymer.
 4. Thecomposition according to claim 1, wherein the vulcanizing agent (b) isselected from the group consisting of1,1-bis(t-butylperoxy)-3,5,5-trimethylcyclohexane,2,5-dimethylhexane-2,5 dihydroxyperoxide, di-t-butyl peroxide, t-butylcumyl peroxide, dicumyl peroxide,α,α'-bis(t-butylperoxy)-p-diisopropylbenzene,2,5-dimethyl-2,5-di(t-butylperoxy)hexane,2,5-dimethyl-2,5-di(t-butylperoxy)hexyne -3, benzoyl peroxide,t-butylperoxybenzene, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane,t-butylperoxymaleic acid and t-butylperoxyisopropyl carbonate.
 5. Thecomposition according to claim 1, wherein the compound of the formula(I) is selected from the group consisting of 2-t-butyl-4-methoxyphenol,3-t-butyl-4-methoxyphenol, 2-t-butyl-4-ethoxyphenol,3-t-butyl-4-ethoxyphenol, 2-t-butyl-4-propoxyphenol,3-t-butyl-4-propoxyphenol, 2-( 1,1 -diethylpropyl)-4-methoxyphenol,3-(1,1 -diethylpropyl) -4-methoxyphenol, 2-( 1,1 -dipropylbutyl)-4methoxyphenol, 3-( 1,1 -dipropylbutyl)-4-methoxyphenol, 2-(1,1-diethylpropyl)-4-ethoxyphenol, 3-(1,1-diethylpropyl)-4-ethoxyphenol, 2-( 1,1-dipropylbutyl)-4-ethoxyphenol, 3-( 1,1 -dipropylbutyl)-4 ethoxyphenol,2-( 1,1 -diethylpropyl)-4-propoxyphenol and 3-(1,1-diethylpropyl)-4-propoxyphenol.
 6. The composition according toclaim 1, wherein the composition further contains a crosslinking aid (d)and the crosslinking aid (d) has at least two groups which are selectedfrom the group consisting of CH₂ ═CH-- group, CH₂ ═CH--CH₂ -- group andCF₂ ═CF-- group.
 7. The composition according to claim 6, wherein theamount of the crosslinking aid (d) is from 0.1 to 5.0 parts by weightper 100 parts by weight of the fluororubber (a).
 8. A cured materialprepared by vulcanizing the composition according to claim 1.